1. Field of the Invention
The present invention relates to a rotary type electric shaver including an outer cutter(s) having a shaving surface on an upper surface of a ring-shaped thin layer portion thereof and an inner cutter(s) rotationally making sliding contact from below with the lower surface of the thin layer portion of the outer cutter(s), thus cutting whiskers (hair) advancing into a hair introduction opening formed in the thin layer portion.
2. Description of the Related Art
In an electric shaver of the type as described above, hair introduction openings are formed so as to transect the thin layer portion of an outer cutter in substantially the radial direction, and the hair introduction openings are formed in a slit shape of substantially constant width. Each hair introduction opening (“slit”) conventionally has side wall surfaces that are perpendicular to the upper surface of the thin layer portion of the outer cutter in cross section that is substantially orthogonal to the lengthwise direction of the elongated opening. In other words, the shearing angle (cutting edge angle of the outer cutter), which is formed by the side wall surface of the hair introduction opening on the forefront side of the inner cutter rotational direction and by the inner cutter rotational direction near its lower end, is the right angles, as disclosed in Japanese Patent Application Laid-Open (Kokai) Nos. S57-31888 and S63-194691.
FIG. 7 shows, in a simple manner, the shape of hair introduction openings in cross-section substantially orthogonal to the lengthwise direction of the hair introduction openings. In FIG. 7, the reference numeral 1 is an outer cutter, and slit-shaped hair introduction openings 2 are located between neighboring ribs 3 and 3. The reference numeral 4 is an inner cutter, and this inner cutter 4 rotates in the direction of arrow F. In other words, arrow F is the rotational direction of the inner cutter (or the inner cutter rotational direction).
In this shown outer cutter 1 of the prior art, the shearing angle a (a cutting edge angle of the outer cutter 1), which is formed by the side wall surface 5 of the hair introduction opening 2 on the forefront side in the direction F of the rotation of the inner cutter 4 (or on the forefront side of the inner cutter rotational direction F) and by the inner cutter rotational direction F, is 90° (right angles). The cutting edge angle b, which is a shearing angle formed by the cutter (front) surface 6 of the inner cutter 4 on the leading edge side of the inner cutter rotational direction F and by the top end surface of the inner cutter 4, is an acute angle.
With the outer cutter 1 of the conventional rotary type electric shaver as shown in FIG. 7, the cutting edge angle a of the outer cutter 1 is 90° or is at the right angles with respect to the undersurface of the rib 3 with which the top end surface of the inner cutter 4 makes sliding contact. As a result, a whisker (hair) 7 that entered the hair introduction opening 2 touches the cutting edge 8 (tip of the cutting edge angle a) of the outer cutter 1 and is positioned there, thus being cut by the cutting edge 9 of the rotating inner cutter 4. In other words, the cutting edge 8 of the outer cutter 1 mainly functions to hold or support the hair 7 but does not actively contribute to cut the hair 7. As a result, the shaver cannot provide sharp and clean shaving.